Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$170.25	9.592%	$186.5804	$186.58	$186.60	$186.60
Purchase #2	$104.77	9.479%	$114.7011	$114.70	$114.70	$114.70
Purchase #3	$101.46	4.413%	$105.9374	$105.94	$105.95	$105.90
Purchase #4	$206.30	12.196%	$231.4603	$231.46	$231.45	$231.50
Purchase #5	$177.87	9.224%	$194.2767	$194.28	$194.30	$194.30
Purchase #6	$147.83	5.343%	$155.7286	$155.73	$155.75	$155.70
Purchase #7	$98.69	13.176%	$111.6934	$111.69	$111.70	$111.70
7 purchase totals =	$1,007.17		$1,100.3779	$1,100.38	$1,100.45	$1,100.40